Atherosclerosis and cardiovascular disease are leading causes of mortality and morbidity worldwide. Each process can affect major and minor arterial vessels. Yet while arterial and venous thrombosis have numerous origins, it is at the end organs where the effects of the thrombosis are most felt and where those effects result in clinical manifestation. Arterial thrombosis, for example, may manifest as sudden cardiac death, acute coronary syndromes (ACS), stroke, or peripheral embolization. Venous thrombosis may manifest as acute deep vein thrombosis (DVT), pulmonary embolism (PE), or paradoxical arterial embolization.
The underlying causes of these manifestations range from atherosclerosis due to plaque rupture or erosion (e.g., sudden death, ACS, etc), cardiac embolization from atrial fibrillation or left ventricular aneurysm (often secondary to coronary atherosclerosis), stasis and immobility (e.g., postoperative DVT), hypercoagulable state (activated protein C deficiency, malignancy), and a variety of rare disorders. Furthermore, thrombosis may complicate the performance of cardiovascular procedures or initiate malfunction of foreign devices implanted in the cardiovascular system (heart valves, arterial stents, venous filters, bypass grafts, etc).
Given the deleterious impact of atherosclerosis, various interventions have been developed to reduce or remove blockages in blood vessels. One technique for treating stenosis or occlusion of a blood vessel is balloon angioplasty. A balloon catheter is inserted into the narrowed or blocked area, and the balloon is inflated to expand the constricted area. While commonly performed, this method is not without risk. Angioplasty can be associated with significant plaque shift, arterial dissection and high risk of restenosis.
Coronary bypass surgery is another more costly and invasive form of intervention, in which a section of a vein, such as the saphenous vein taken from the leg, is used to form a connection between the aorta and the coronary artery distal to the obstruction. Though common, this intervention is not without challenges. Over time, the saphenous vein graft may itself become diseased, stenosed, or occluded similar to the bypassed vessel, which can present a different problem, as atherosclerotic plaque in saphenous vein grafts tends to be more friable and less fibrocalcific than its counterpart in native coronary arteries.
Various types of stents have been designed to address the problems of restenosis discussed above, generally with good success. However, while the stents have, in many ways, revolutionized the field of vascular interventions, significant challenges remain. Bifurcations and ostial lesions, for example, present unique problems to surgeons during a stenting procedure. In coronary and non-coronary beds, the ostial location is prone to develop atherosclerosis and is therefore the most common site of disease in renal vessels and is a common site of disease in patients with saphenous vein graft disease or those with coronary artery disease. In endovascular treatment of ostial lesions, it is desirable to adequately cover the entire vessel ostium but to do so without leaving excessive stent protruding from the ostial vessel into the aorta or main vessel. This is desirable for a number of reasons. If the ostium is missed, there is a high risk of restenosis. Further still, if the ostium is missed, it is difficult to identify which portion of the entire opening has been affected and which has not, thus requiring an entirely new stenting procedure and possibly a new stent altogether. Another problem is that if the stent protrudes too far into the aorta or main vessel, it will become difficult to subsequently re-engage the vessel with a diagnostic catheter. Although there is a low risk of restenosis from having the stent extending too far into the main vessel, the procedure is made more difficult because the catheter guide wire will often go through a strut member limiting the effectiveness of the guidewire for the catheter upon entry and removal. Thus, future interventions are made difficult or next to impossible to implement.
The most common ostial intervention sites, including bifurcation points, are aortic-coronary ostia and renal ostia. The standard angioplasty balloon used for such sites is a semi-compliant or non-compliant balloon that is fixed to a balloon shaft and can be expanded and deflated as is in routine interventional practice. The balloon will often have radiopaque markers that are used to identify the proximal and distal ends of the balloon and that serve to guide the location of the proximal and distal edge of the stent. Radiographic location techniques, using multiple angulations and contrast, identify the ostium of the vessel. This practice unfortunately translates into extra-radiation to the patient and the operator and also carries the burden of increased contrast and prolonged occlusion of the vessel. This practice also increases the risk of the procedure failing especially for patients undergoing interventions on ostia of the main coronary arteries or ostia of the saphenous vain grafts. In patients with renal dysfunction, for example, the extra contrast volume and radiation exposure can translate into renal failure and the need for dialysis.
In any event, there is a need for improved stenting devices for ostial lesions, in particular, and at bifurcation points to allow more accurate alignment of the stent so as to cover the entire ostium and also control the extent to which the stent extends into the main vessel.